Merge branch 'docs/container-registry-api-introduced' into 'master'

Mention when the Registry API was introduced

See merge request gitlab-org/gitlab-ce!24596

(cherry picked from commit c220bee5)

597f4fea Add which GitLab version the Registry API docs were introduced
928fc142 Fix wrong Registry API description

doc/api/container_registry.md

 # Container Registry API
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/issues/55978) in GitLab 11.8.
+
 This is the API docs of the [GitLab Container Registry](../user/project/container_registry.md).
 ## List registry repositories
@@ -42,7 +44,7 @@ Example response:
 ## Delete registry repository
-Get a list of repository commits in a project.
+Delete a repository in registry.
 This operation is executed asynchronously and might take some time to get executed.